A laser light source module uses at least one semiconductor laser device as a light source. In the laser light source module, a light-collecting optical system collects laser beams emitted from the light source, and inputs the laser beams into an optical element such as an optical fiber. To protect the semiconductor laser device from oxidation, a cap is put on the semiconductor laser device or a semiconductor laser array, a lens barrel is located so as to surround the cap, and a light-collecting optical system is provided on a top of the lens barrel.
In a laser light source module having such a configuration, the calorific value from its semiconductor laser device is relatively high, and particularly the calorific value of a semiconductor laser array having a plurality of semiconductor laser devices is considerably high. When a high-power laser light source module using a semiconductor laser array as a light source is continuously used with high power without releasing heat, the semiconductor laser devices are degraded by heat generated by their own, and thus lifetime thereof is shortened considerably. Therefore, it is necessary to provide an efficient heat-releasing mechanism.
If a semiconductor laser array is mounted on a heat sink made of a copper-based material, the heat-releasing efficiency is enhanced; however, when the amount of the copper-based material used in the laser light source module is increased, the mechanical strength of the module is lowered and the cost of the module is increased. For this reason, many laser light source modules employ such a configuration that a semiconductor laser array is mounted on a stem made of an inexpensive iron-based material having high mechanical strength, and a heat sink made of a copper-based material is provided on the stem.
For example, Patent Document 1 discloses a method for manufacturing a stem with a heat sink in which the heat sink having an element-fixing surface is integrally formed on an iron eyelet by press-fitting a copper heat-sink forming material into a through hole or a recess formed in the eyelet. According to this manufacturing method, the heat sink and the eyelet can be integrally formed together without using brazing filler metal.
Patent Document 2 discloses a laser diode package stem in which a coupling groove whose width is increased from the bottom toward the top is formed in a stem, a copper rod member is inserted into the coupling groove, and the rod member is then struck in a row by a predetermined die, thereby expanding the rod member in the coupling groove, fixing the rod member to the stem, and forming the rod member into a heat sink. In the laser diode package stem, a laser diode is mounted on an upper surface of the heat sink.
In the laser light source module having the iron stem and the copper heat sink, because a coefficient of linear expansion of iron and a coefficient of linear expansion of copper are different from each other, a relatively large thermal stress acts on bonded portions between the stem and the heat sink due to temperature rise caused by an operation of the semiconductor laser device. If the heat sink is press-fitted into the stem, it is possible to prevent the stem and the heat sink from being separated from each other by a thermal stress.    Patent Document 1: Japanese Patent Application Laid-open No. H10-116943    Patent Document 2: Japanese Patent Application Laid-open No. 2005-223302